AIDS has reached epidemic proportions worldwide and the development of a vaccine appears the most effective approach to curbing HIV-1 infection worldwide. Current HIV-specific antigens used to elicit T cell responses included recombinant vaccinia viruses, recombinant whole proteins or synthetic peptides, many of which are not available in non-B subtypes. These issues raise significant obstacles to conducting vaccine and HIV immunology studies in resource-poor countries. This grant intends to evaluate a novel HIV antigen expression vector that might obviate the use of recombinant vaccinia viruses or large pools of overlapping synthetic peptides. We evaluated genetically detoxified lethal toxin of Bacillus anthracis containing HIV-1 antigen (LFn-HIV) and found that CTL responses are reproducibly detectable. Production of LFn-HIV containing HIV antigens up to 500 amino acids is technically simple, relatively inexpensive, and is, therefore, an attractive alternative source of non-B clade antigens as well as multiple-epitopes construct. We therefore propose to evaluate LFn-HIV in both functional and quantitative assays to study the cellular immune response. This technology will be explored to address the efficacy of antigen expression as well as potential pathway of the antigen processing and presentation, and finally introduce the concept in Uganda to begin evaluating cross-clade immune response. The specific aims of this proposal are: 1) To develop and test a new MHC class I antigen delivery system using genetically detoxified anthrax lethal factor. We will begin to develop and test subtype A and D constructs using well defined CTL cell lines or clones from Uganda. 2) To evaluate the antigen processing and presentation of LFn-HIV. We will identify the optimal LFn sequence required for cytosolic entry. We will also determine whether different APCs express LFn-HIV more efficiently. Finally we will explore whether LFn-HIV elicits T helper response and whether this antigen processing pathway is partially shared with the MHC class I pathway. 3) To test the LFn-HIV in a resource-limited setting such as Uganda. We will introduce the use of LFn-HIV of multiple clades (A, B and D) and assess the level of cross-clade activity in this population using both ELIspot and flow based cytometry.